Orthogonal Frequency Division Multiplexing (OFDM) employing orthogonal frequency domain modulation is a popular modulation technique for wireless communications. It has been adopted in standards for technologies such as wireless networks (802.11a/g), digital television broadcasting (DVB-T/S/H and ISDB-T), and broadband wireless local loops (802.16e/WiMax). An OFDM wireless transmitter broadcasts information consisting of symbols to an OFDM receiver employing a wireless communication channel between the transmitter and the receiver. The characteristics of this communication channel typically vary over time due to changes in the transmission path. The performance of the entire communication system hinges on the ability of the receiver to establish a reliable representation of the transmitted symbol. This necessitates that the receiver provide an appropriate channel estimate of the transmission channel.
In OFDM communication systems, channel equalization is performed in the frequency domain. Each block of data is preceded by a cyclic prefix, ensuring that the sub-carriers generated by a discrete Fourier transform (DFT) of a properly chosen block of data are orthogonal. This allows a linear time-invariant channel to be equalized in the frequency domain. Practical OFDM communication systems estimate the channel using values provided from a set of pilot tones. The receiver generates samples of the channel's frequency response by dividing the received values at these tones by the modulated training data. The channel estimates at the data tones are estimated from these samples.
The estimates can be generated by two-dimensional interpolation over a number of buffered OFDM symbols. The interpolation may be broken into two stages consisting of time interpolation followed by frequency interpolation. However, interpolation errors and the effect of additive noise during the channel estimation process degrade the quality of the communication channel. This, in turn, reduces the overall performance of the communication system.
Accordingly, what is needed in the art is a more effective way to overcome the effects of interpolation errors and additive noise in channel estimation.